POPULATION DYNAMICS AND LIFE HISTORY OF CREPIDULA CONVEXA SAY (GASTROPODA: PROSOBRANCHIA) IN DELAWARE BAY

¹ Rutgers—The State University, New Brunswick, New Jersey
² Biological Sciences Group, University of Connecticut, Storrs, Connecticut 06268

1. The reproductive biology and population dynamics of two substrate forms Crepidula convexa were investigated. The species is a protandric hemaphrodite with direct development.

2. The egg mass differs from other species in the genus in that the capsules comprising it are compartmentalized in early development. Later, the compartment walls break down and there is a decrease in the number of embryos, suggesting the existence of "embryonic cannibalism." Size-specific fecundity of the Deleware Bay population appears higher than published data for a Woods Hole population.

3. There is rarely more than one male associated with a female and the ratio of males to females is low.

4. Life span is at least two seasons. At the beginning of June, when reproduction is maximal, the population is predominantly female. The resulting influx of juveniles shifts the sexual composition of the population in such a way that males dominate by August. The transformation of these males to females during the winter gradually shifts the sexual composition so that females again predominate by Spring.

5. Crepidula convexa living on Pagurus form a dwarf population which differs from cultch animals in morphology, mating behavior, breeding cycle and maturation rate. These differences are attributed to limitations of substrate. Exchange of individuals between subpopulations is facilitated by phoresis on hermit crabs.

6. The high mobility of young C. convexa, which makes phoresis possible, is considered to be the key factor in the success of this species in the colonization of virgin substrates, thus facilitating dispersal in the absence of a larval stage. The capacity of males to fertilize more than one female is also a function of this mobility and is probably the major factor in maintaining a sex ratio (males < females) which favors maximal reproduction.